A special edition for those who enjoy homebrewing the radios they use to listen to DX
Radio Havana Cuba Dxers Unlimited Dxers Unlimited's mid week edition for 6-7 March 2007 By Arnie Coro radio amateur CO2KK Hi amigos radioaficionados, with our now traditional salute, we are now starting up the mid week edition of your favorite radio hobby program, via short wave and also available from www radiohc dot cu from 05 to 07 UTC... I am Arnie Coro, radio amateur CO2KK, that's my ham radio callsign, and yes I do enjoy a lot operate on CW, Single sideband and Digital Modes on the HF bands, and also watching for those elusive but nice and challenging sporadic E openings that area about to begin in just a few weeks here in the Northern Hemisphere. Homebrew receivers, radios that are built from electronic components and that you assemble yourself, bring in signals that have a special sound of sorts, special in the sense that when signals come out trough headphones or loudspeakers of those homebrew radios that started to operate after many hours of a unique learning experience, you feel a sense of accomplishment second to none. And let me add that after many years of homebrewing radios, from the simplest to the most sophisticated, by homebrew receivers keep that special sound all the time!!! For example, my prototype vacuum tube regenerodyne, originally built fifteen years ago, is still a joy to operate. All along its life, I have done a lot of experiments with it by changing the tuning coils, the values of some critical components and even vacuum tube types, so it has acted as a test bed of sorts... But, it still gets used , especially during the weekends, when on Sunday mornings I enjoy operating on the 40 meters band using the single side band voice mode to talk to my many friends all along the Cuban archipelago that are active on the several nets operated by provincial radio clubs.. My prototype regenerodyne has one of the plug in coils optimized for covering just the lower 150 kiloHertz of 40 meters, where the nets operate. For those of you that have sent e-mail messages, letters and postcards wanting to know more about the original regenerodyne prototype, it will be our number one feature today here at Dxers Unlimited's mid week edition... Stay tuned, and write down my e-mail address to send your signal reports and comments about the program as well as any radio hobby related questions you may have in mind... mail to [EMAIL PROTECTED], again [EMAIL PROTECTED], or send your postcards and letters VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana Cuba... I'll be back in just a few seconds amigos !!! ..... Si amigos, this is Radio Havana Cuba, the name of the show is Dxers Unlimited and today our number one most popular section ASK ARNIE , will be providing you with a detailed description of not one , but two regenerative receivers that are rather easy to homebrew and provide excellent performance... First you will listen to the data about the original version of the KK-12 REGENERODYNE vacuum tube multi band receiver and then I will be describing the Desert Rat Three, a solid state 1996 design, that is, according to all my tests the best solid state simple regenerative circuit design , the brainchild of well known American radio amateur and short wave listener Paul Harden NA5N Now let's start with the KK-12 Regenerodyne that so many of you have asked about lately. The final version of this radio receiver uses a dual tuned bandpass input filter and signal attenuator, that is connected to the grid of a radio frequency amplifier vacuum tube that provides very little gain, as its main function is to provide isolation to the mixer stage that follows it. The other signal for the mixer is provided by a simple quartz crystal oscillator that is capable of using many different types of crystals in many different types of holders... So, the front end of the KK-12, is conventional , but very well designed... The output of the mixer is fed to the variable frequency regenerative detector stage,that uses a Hartley type detector with screen grid voltage regeneration control...The audio output from the detector is fed to a two stage audio amplifier, that in the original prototype was made using two individual vacuum tubes that were at hand, a 6C5 and a 6V6. But the latest version , which is the one in use now uses a triode-pentode vacuum tube contained inside the same glass envelope. Summarizing, the vacuum tube line up is as follows, a 6BA6 or similar pentode RF amplifier stage , a 12AT7 or the equivalent ECC81 in a Pullen Mixer configuration , a 12AT7 crystal oscillator and cathode follower, a 6BA6 or similar regenerative detector and a ECL82 or similar audio pre-amp and audio power amplifier stage. The radio uses a homebrew solid state power supply with some special characteristics... Its maximum B + voltage is 140 volts DC, it provides plus 75 volts regulated DC for feeding the regenerative detector stage, and 6 volts DC for the detector's and the audio amplifier stages filaments, in order to keep the presence of 120 cycle HUM really low. With today's solid state diodes and integrated circuit voltage regulators plus the availability of high values of electrolytic capacitors, this power supply is almost like powering the receiver from a pair of B batteries and an accumulator for the filaments, like in the early days of radio, but without having to worry about changing the B plus batteries or recharging the accumulator !! The radio was built without any attempt to make it a compact or miniature set, plenty space was left between the parts, so as to make experimenting easier. The regenerative detector in this final version is capable of tuning to several frequency ranges... With one "bandspread coil" it tune from 2.0 to 2.15 megaHertz, that is from 2000 kiloHertz to two thousand one hundred and fifty kiloHertz, that when mixed with a 5 megaHertz crystal provide excellent bandspread coverage of the first one hundred and fifty kilohertz of the 40 meters amateur band, changing the crystal to 8 megaHertz, that by the way is a very common computer surplus quartz crystal, the the radio tunes to the 30 meters band, and provides you with a nice propagation indicator, as you can pick up the time and frequency standard stations that operate on 10 megaHertz, that serve as a reliable calibration source...A third crystal, that oscillates on 12 megaHertz provides reception on the first half of 20 meters, making reception of CW stations found at the low end of 20 very easy. But the KK-12's plug in detector coils feature also gives you the possibility of tuning to one or two megahertz wide segments of the short wave spectrum. Changing the detector coil to the general coverage one, and using the 5 megaHertz crystal, you can tune from seven to eight megaHertz , or from three to four megahertz according to the setting of the bandpass input tuning filter... Every crystal offers the possibility of two tuning ranges, one that comes out when you add the frequency of the crystal to the frequency of the detector, and the other one, that appears when you subtract the frequency of the detector from the frequency of the quartz crystal. Let me add, that this is a "hands on the controls" radio, that requires the operator to tune in the radio frequency front end filter, the detector's frequency and the regeneration control. In the KK-12 design regeneration is so smooth,that once set for CW or Single sideband reception you can just leave it there, and when you want to do pick up some international short wave broadcast stations like Radio Havana Cuba, the only thing you have to do is back up the regeneration control a bit to listen to standard AM plus carrier signals... Si amigos, yes my friends, homebrewing the KK-12 is a very nice project,and when properly built, this radio has an amazing sensitivity and selectivity !!!, so good in fact, that one of my favorite demonstrations is to connect the KK12 and my Kenwood TS820 to the same antenna by means of a coaxial switch, and show visitors at CO2KK how the two radios pick up a weak signal on 40 meters... something that usually leads to them leaving my home with the KK-12 schematic diagram and step by step building instructions !!! ........ This is Radio Havana Cuba,the name of the show is Dxers Unlimited, and yes amigos, you can receive our nice QSL card, just send a signal report and comments about this program to [EMAIL PROTECTED], again [EMAIL PROTECTED] or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba Havana, Cuba, and now here is as promised, ASK ARNIE part two, a brief description of the Desert Rat Three, NA5N's solid state regenerative receiver... It uses a simple untuned RF stage for isolation, a regenerative RF stage , an emitter follower , a germanium diode detector, two audio amplifier stages and at the tail end, an integrated circuit audio amplifier. The original circuit is designed for tuning between 6 and 15 megaHertz with a single coil that is wound on a small length of plastic tubing, so there is no need to search for hard to find ferrite toroid cores. Tests done by the author, show that the receiver is capable of picking up a mininimum detectable signal level of minus 105 dB referenced to one microvolt on CW, while on the AM mode, the sensitivity is -93 dB or 5 microvolts... The Desert Rat 3 uses very common transistors, nothing rare or hard to find here, and I have built several of them without using a single new from the box electronic component, in other words they were built using just recycled parts !!! Ah, before I forget, the same original tuning coil, when shunted by an extra 100 picofarads capacitor , provides a more limited coverage tuning range from 5.5 to 7.5 megaHertz, so you have more bandspread when tuning to the 49 and 41meters international broadcast bands and the 40 meters ham band... I am now working on new easy to see schematic diagrams for both the KK-12 regenerodyne and the Desert Rat 3, so you can send your request for both of them via e-mail to [EMAIL PROTECTED], and I'll add you to the mailing list !!! And now amigos as always at the end of Dxers Unlimited, when I am here in Havana, your welcome to listen to Arnie Coro's HF plus low band VHF propagation update and forecast .. Solar flux is at rock bottom baseline level of 70 flux units, and there are chances for some high latitude propagation disturbances to happen, The effective sunspot number is just 17 units, so the daytimemaximum useable frequency curve keeps staying below the 22 or 23 megaHertz marker even at peak times... After Thursday HF propagation will improve a bit, with better chances for nice equinoctial DX on the AM broadcast and the Tropical bands... Hope to have you all listening to the weekend edition of the program and don't forget to send your signal reports, comments about theshow and radio hobby related questions to [EMAIL PROTECTED] or via AIr Mail to Arnie Coro, Radio Havana Cuba, Havana, Cuba. ---[Start Commercial]--------------------- Preorder your WRTH 2007: http://www.hard-core-dx.com/redirect2.php?id=wrth2007 ---[End Commercial]----------------------- ________________________________________ Hard-Core-DX mailing list [email protected] http://montreal.kotalampi.com/mailman/listinfo/hard-core-dx http://www.hard-core-dx.com/ _______________________________________________ THE INFORMATION IN THIS ARTICLE IS FREE. It may be copied, distributed and/or modified under the conditions set down in the Design Science License published by Michael Stutz at http://www.gnu.org/licenses/dsl.html
